gdb: implement inferior-specific breakpoints

This is a "workaround feature" which is intended to help with
multi-target program debugging until a more fundamental solution is
available.

With this addition, the following command syntax is recognized by gdb:

(gdb) b file.c:42 inferior 1

It willl only insert breakpoint locations into program space that
matches inferior 1 and will only consider a breakpoint hit if the
current inferior is 1.

It is already possible to achieve similar results by using
`if $_inferior == N` conditional breakpoint, but the major advantage of
the implemented feature is that it skips insertion of breakpoints
completely, which can be of a high importance for some platforms.

gdb/ChangeLog:
2019-11-20  Mihails Strasuns  <mihails.strasuns@intel.com>

	* breakpoint.h (struct breakpoint): new field 'inferior'
	* breakpoint.c (find_condition_and_thread): supports new
	break command syntax for specifying an inferior
	(create_breakpoint): pass breakpoint inferior argument around
	(decode_location_default, init_breakpoint_sal): if inferior number is
	present, only match location if inferior pspace matches
	location pspace
	(print_one_breakpoint_location): always print inferior for
	inferior-specific breakpoints
	* linespec.c (linespec_keywords): add "inferior" to the keyword list

gdb/testsuite/ChangeLog:
2019-11-20  Mihails Strasuns  <mihails.strasuns@intel.com>

	* gdb.base/breakpoint-inferior.exp: new test case to cover
	functionaity of inferior breakpoint feature
	* lib/completion-support.exp, gdb.linespec/explicit.exp:
	recognize new keyword

Signed-off-by: Mihails Strasuns <mihails.strasuns@intel.com>

gdb/breakpoint.h

@@ -654,7 +654,7 @@ struct breakpoint_ops
 				  gdb::unique_xmalloc_ptr<char>,
 				  gdb::unique_xmalloc_ptr<char>,
 				  enum bptype, enum bpdisp, int, int,
-				  int, int, const struct breakpoint_ops *,
+				  int, int, int, const struct breakpoint_ops *,
 				  int, int, int, unsigned);
 
   /* Given the location (second parameter), this method decodes it and
@@ -810,6 +810,10 @@ struct breakpoint
      care.  */
   int task = 0;
 
+  /* GDB inferior ID number for inferior-specific breakpoint, or 0
+     if don't care.  */
+  int inferior = 0;
+
   /* Count of the number of times this breakpoint was taken, dumped
      with the info, but not used for anything else.  Useful for seeing
      how many times you hit a break prior to the program aborting, so
@@ -1294,6 +1298,10 @@ struct breakpoint_deleter
   }
 };
 
+/* Deletes all breakpoints with an inferior condition which
+   have an inferior number match the argument.  */
+extern void delete_breakpoints_inf (struct inferior*);
+
 typedef std::unique_ptr<struct breakpoint, breakpoint_deleter> breakpoint_up;
 
 extern breakpoint_up set_momentary_breakpoint
@@ -1562,6 +1570,8 @@ extern void breakpoint_set_silent (struct breakpoint *b, int silent);
 
 extern void breakpoint_set_thread (struct breakpoint *b, int thread);
 
+extern void breakpoint_set_inferior (struct breakpoint *b, int inferior);
+
 extern void breakpoint_set_task (struct breakpoint *b, int task);
 
 /* Clear the "inserted" flag in all breakpoints.  */

gdb/c-exp.y

@@ -2953,11 +2953,13 @@ lex_one_token (struct parser_state *par_state, bool *is_quoted_name)
   /* For the same reason (breakpoint conditions), "thread N"
      terminates the expression.  "thread" could be an identifier, but
      an identifier is never followed by a number without intervening
-     punctuation.  "task" is similar.  Handle abbreviations of these,
-     similarly to breakpoint.c:find_condition_and_thread.  */
+     punctuation.  "task" and "inferior" are similar.  Handle
+     abbreviations of these, similarly to
+     breakpoint.c:find_condition_and_thread.  */
   if (namelen >= 1
       && (strncmp (tokstart, "thread", namelen) == 0
-	  || strncmp (tokstart, "task", namelen) == 0)
+	  || strncmp (tokstart, "task", namelen) == 0
+	  || strncmp (tokstart, "inferior", namelen) == 0)
       && (tokstart[namelen] == ' ' || tokstart[namelen] == '\t')
       && ! scanning_macro_expansion ())
     {

gdb/doc/gdb.texinfo

@@ -4417,8 +4417,9 @@ C@t{++}, a function name may refer to more than one possible place to break.
 that situation.
 
 It is also possible to insert a breakpoint that will stop the program
-only if a specific thread (@pxref{Thread-Specific Breakpoints})
-or a specific task (@pxref{Ada Tasks}) hits that breakpoint.
+only if a specific thread (@pxref{Thread-Specific Breakpoints}),
+a specific task (@pxref{Ada Tasks}) or a specific inferior
+(@pxref{Inferior-Specific Breakpoints}) hits that breakpoint.
 
 @item break
 When called without any arguments, @code{break} sets a breakpoint at
@@ -6918,6 +6919,7 @@ you examine the stopped thread in the debugger.
 * Non-Stop Mode::		Other threads continue to execute
 * Background Execution::	Running your program asynchronously
 * Thread-Specific Breakpoints::	Controlling breakpoints
+* Inferior-Specific Breakpoints::	Controlling breakpoints
 * Interrupted System Calls::	GDB may interfere with system calls
 * Observer Mode::               GDB does not alter program behavior
 @end menu
@@ -7252,6 +7254,44 @@ Process}), or if @value{GDBN} loses the remote connection
 explictly asks for the thread list with the @code{info threads}
 command.
 
+@node Inferior-Specific Breakpoints
+@subsection Inferior-Specific Breakpoints
+
+It is also possible to limit breakpoints to specific inferior program space,
+which can be especially useful when doing multi-target debugging with some
+source files shared between targets.
+
+@table @code
+@cindex breakpoints and inferiors
+@cindex inferior breakpoints
+@kindex break @dots{} inferior @var{inferior-num}
+@item break @var{location} inferior @var{inferior-num}
+@itemx break @var{location} inferior @var{inferior-num} if @dots{}
+@var{location} specifies source lines; there are several ways of
+writing them (@pxref{Specify Location}), but the effect is always to
+specify some source line.
+
+Use the qualifier @samp{inferior @var{inferior-num}} with a breakpoint command
+to specify that you only want @value{GDBN} to stop the program if execution
+happens in a context of the specified inferior.  The @var{inferior-num} number
+is one of the inferior numbers as shown by @samp{info inferior} command output.
+
+One major difference compared to @pxref{Thread-Specific Breakpoints} is that
+inferior specific breakpoints won't be inserted at all for other inferiors and
+thus won't be shown by the @samp{info break} command.
+
+If inferior gets removed while inferior-specific breakpoint is present, a
+warning will be printed and the breakpoint will never be hit.
+
+You can use the @code{inferior} qualifier with the other qualifiers and
+conditionals too:
+
+@smallexample
+(@value{GDBP}) break frik.c:13 inferior 1 thread 2 if bartab > lim
+@end smallexample
+
+@end table
+
 @node Interrupted System Calls
 @subsection Interrupted System Calls 
 

gdb/doc/python.texi

@@ -5943,6 +5943,12 @@ thread's global id.  If the breakpoint is not thread-specific, this
 attribute is @code{None}.  This attribute is writable.
 @end defvar
 
+@defvar Breakpoint.inferior
+If the breakpoint is inferior-specific, this attribute holds the inferior
+number.  If the breakpoint is not inferior-specific, this attribute is
+@code{None}.  This attribute is writable.
+@end defvar
+
 @defvar Breakpoint.task
 If the breakpoint is Ada task-specific, this attribute holds the Ada task
 id.  If the breakpoint is not task-specific (or the underlying

gdb/inferior.c

@@ -193,6 +193,8 @@ inferior::clear_thread_list (bool silent)
 void
 delete_inferior (struct inferior *inf)
 {
+  delete_breakpoints_inf (inf);
+
   inf->clear_thread_list (true);
 
   auto it = inferior_list.iterator_to (*inf);

gdb/linespec.c

@@ -255,7 +255,9 @@ typedef enum ls_token_type linespec_token_type;
 
 /* List of keywords.  This is NULL-terminated so that it can be used
    as enum completer.  */
-const char * const linespec_keywords[] = { "if", "thread", "task", "-force-condition", NULL };
+const char * const linespec_keywords[] = { "if", "thread", "task",
+					   "-force-condition",
+					   "inferior", NULL };
 #define IF_KEYWORD_INDEX 0
 #define FORCE_KEYWORD_INDEX 3
 

gdb/python/py-breakpoint.c

@@ -250,6 +250,48 @@ bppy_set_thread (PyObject *self, PyObject *newvalue, void *closure)
   return 0;
 }
 
+/* Python function to set the inferior of a breakpoint.  */
+static int
+bppy_set_inferior (PyObject *self, PyObject *newvalue, void *closure)
+{
+  gdbpy_breakpoint_object *self_bp = (gdbpy_breakpoint_object *) self;
+  long num;
+
+  BPPY_SET_REQUIRE_VALID (self_bp);
+
+  if (newvalue == NULL)
+    {
+      PyErr_SetString (PyExc_TypeError,
+		       _("Cannot delete `inferior' attribute."));
+      return -1;
+    }
+  else if (PyInt_Check (newvalue))
+    {
+      if (! gdb_py_int_as_long (newvalue, &num))
+	return -1;
+
+      if (find_inferior_id (num) == nullptr)
+	{
+	  PyErr_SetString (PyExc_RuntimeError,
+			   _("Invalid inferior number."));
+	  return -1;
+	}
+    }
+  else if (newvalue == Py_None)
+    num = 0;
+  else
+    {
+      PyErr_SetString (
+	PyExc_TypeError,
+	_("The value of `inferior' must be an integer or None."));
+      return -1;
+    }
+
+  breakpoint_set_inferior (self_bp->bp, num);
+
+  return 0;
+}
+
 /* Python function to set the (Ada) task of a breakpoint.  */
 static int
 bppy_set_task (PyObject *self, PyObject *newvalue, void *closure)
@@ -656,6 +698,20 @@ bppy_get_thread (PyObject *self, void *closure)
   return gdb_py_object_from_longest (self_bp->bp->thread).release ();
 }
 
+/* Python function to get the breakpoint's inferior number.  */
+static PyObject *
+bppy_get_inferior (PyObject *self, void *closure)
+{
+  gdbpy_breakpoint_object *self_bp = (gdbpy_breakpoint_object *) self;
+
+  BPPY_REQUIRE_VALID (self_bp);
+
+  if (self_bp->bp->inferior == 0)
+    Py_RETURN_NONE;
+
+  return gdb_py_object_from_longest (self_bp->bp->inferior).release ();
+}
+
 /* Python function to get the breakpoint's task ID (in Ada).  */
 static PyObject *
 bppy_get_task (PyObject *self, void *closure)
@@ -1230,6 +1286,11 @@ static gdb_PyGetSetDef breakpoint_object_getset[] = {
     "Thread ID for the breakpoint.\n\
 If the value is a thread ID (integer), then this is a thread-specific breakpoint.\n\
 If the value is None, then this breakpoint is not thread-specific.\n\
+No other type of value can be used.", NULL },
+  { "inferior", bppy_get_inferior, bppy_set_inferior,
+    "Inferior number for the breakpoint.\n\
+If the value is an integer, then this is an inferior-specific breakpoint.\n\
+If the value is None, then this breakpoint applies to all inferiors.\n\
 No other type of value can be used.", NULL },
   { "task", bppy_get_task, bppy_set_task,
     "Thread ID for the breakpoint.\n\

gdb/testsuite/gdb.base/breakpoint-inferior.c

@@ -0,0 +1,23 @@
+/* This testcase is part of GDB, the GNU debugger.
+
+   Copyright 2019-2020 Free Software Foundation, Inc.
+
+   This program is free software; you can redistribute it and/or modify
+   it under the terms of the GNU General Public License as published by
+   the Free Software Foundation; either version 3 of the License, or
+   (at your option) any later version.
+
+   This program is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+   GNU General Public License for more details.
+
+   You should have received a copy of the GNU General Public License
+   along with this program.  If not, see <http://www.gnu.org/licenses/>.  */
+
+int
+main (void)
+{
+  int i = 1; /* break-here */
+  return 0;
+}

gdb/testsuite/gdb.base/breakpoint-inferior.exp

@@ -0,0 +1,78 @@
+# Copyright 2019-2020 Free Software Foundation, Inc.
+
+# This program is free software; you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation; either version 3 of the License, or
+# (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+standard_testfile
+
+# Check if start command is supported.
+if {[use_gdb_stub]} {
+    return 0
+}
+
+if {[prepare_for_testing "failed to prepare" $testfile $srcfile debug]} {
+    return -1
+}
+
+# Test pending inferior breakpoint
+
+gdb_test "add-inferior"
+set bp_loc [gdb_get_line_number "break-here"]
+gdb_breakpoint "$bp_loc inferior 2" {allow-pending}
+
+gdb_test "inferior 1" "Switching to inferior 1.*" "inferior 1 (pending)"
+if {[gdb_start_cmd] < 0} {
+    fail "start inferior 1"
+    return
+}
+gdb_test "" ".*reakpoint ., main .*${srcfile}.*" "run inferior 1 to main"
+gdb_continue_to_end "inferior 1"
+
+gdb_test "inferior 2"
+gdb_test "file $binfile" "Reading symbols.*" "inferior 2 symbols (pending)"
+if {[gdb_run_cmd] < 0} {
+    fail "run inferior 2"
+    return
+}
+gdb_test_multiple "" "run inferior 2 until bp" {
+    -re -wrap "Breakpoint .*$srcfile:$bp_loc.*" {
+	pass $gdb_test_name
+	gdb_continue_to_end "run inferior 2 until end"
+    }
+    -re -wrap "exited normally" {
+	fail $gdb_test_name
+    }
+}
+
+gdb_test "inferior 1"
+gdb_test "remove-inferiors 2"
+gdb_test "info b" "No breakpoints or watchpoints."
+
+set main_addr [get_hexadecimal_valueof "&main" 0x0]
+gdb_breakpoint "*$main_addr inferior 1"
+gdb_test "add-inferior -exec $binfile" "Reading symbols.*" "inferior 3 symbols"
+gdb_test_multiple "info b" "only inf 1 after location update" {
+    -re -wrap "inf ($decimal)" {
+	set inf_no $expect_out(1,string)
+	gdb_assert {$inf_no == 1} $gdb_test_name
+    }
+}
+gdb_test "set schedule-multiple on"
+if {[gdb_run_cmd] < 0} {
+    fail "run with addr-based bp"
+} else {
+    gdb_test "" "Breakpoint ., main .*${srcfile}.*" "run with addr-based bp"
+}
+
+gdb_test "print \$_inferior" " = 1"
+gdb_continue_to_end "final run to end"

gdb/testsuite/gdb.linespec/explicit.exp

@@ -412,6 +412,7 @@ namespace eval $testfile {
 	    "-qualified"
 	    "-source"
 	    "if"
+	    "inferior"
 	    "task"
 	    "thread"
 	}

gdb/testsuite/gdb.python/py-breakpoint.exp

@@ -104,6 +104,8 @@ proc_with_prefix test_bkpt_basic { } {
 	"Get Breakpoint List" 0
     gdb_test "python print (blist\[1\].thread)" \
 	"None" "Check breakpoint thread"
+    gdb_test "python print (blist\[1\].inferior)" \
+	"None" "Check breakpoint inferior"
     gdb_test "python print (blist\[1\].type == gdb.BP_BREAKPOINT)" \
 	"True" "Check breakpoint type"
     gdb_test "python print (blist\[0\].number)" \
@@ -161,10 +163,12 @@ proc_with_prefix test_bkpt_cond_and_cmds { } {
 
     # Test conditional setting.
     set bp_location1 [gdb_get_line_number "Break at multiply."]
-    gdb_py_test_silent_cmd "python bp1 = gdb.Breakpoint (\"$bp_location1 thread 1\")" \
+    gdb_py_test_silent_cmd "python bp1 = gdb.Breakpoint (\"$bp_location1 thread 1 inferior 1\")" \
 	"Set breakpoint" 0
     gdb_test "python print (bp1.thread == 1)" "True" \
 	"Extra thread spec has been parsed"
+    gdb_test "python print (bp1.inferior == 1)" "True" \
+        "Extra inferior spec has been parsed"
     gdb_continue_to_breakpoint "Break at multiply" \
 	".*Break at multiply.*"
     gdb_py_test_silent_cmd "python bp1.condition = \"i == 5\"" \

gdb/testsuite/lib/completion-support.exp

@@ -27,7 +27,7 @@ namespace eval completion {
     # List of all quote chars, including no-quote at all.
     variable maybe_quoted_list {"" "'" "\""}
 
-    variable keyword_list {"-force-condition" "if" "task" "thread"}
+    variable keyword_list {"-force-condition" "if" "inferior" "task" "thread"}
 
     variable explicit_opts_list \
 	{"-function" "-label" "-line" "-qualified" "-source"}